Hi guys, I'm after some ideas for the recommended brake master cylinder bore size for my 1949 Buick super, I have used the scaredbird disk brake conversion and the front brake callipers are from a 2000 Chevy astro van AWD, the rears are the stock Buick drums. I have emailed mark from scared bird several times now, but he hasn't got back to me. I think I will just go with a universal dual master cylinder but I need to know what bore size first. Cheers Darren
probably depends on if you're using a power booster with it or not. 1-1/8" with power, 1" without, might be a good starting point.
Thanks mate I was going too see how it pulled up before I made the decision on using a booster or not. I have had a 1" in an early falcon with boosted disk front and worked well, but I was curious due to a much bigger car. Cheers Check out my 49 Buick sedanette build
1" is perfect for manual . you can try a 15/16th for more aplication pressure ( at the wheels) but smaller than that you need a booster to help .
I was thinking that you would use a small dia master for manual and a large dia for a power set up but maybe I have it backwards.
In general terms, If you decrease the size of the Master cylinder you increase pressure to the wheel cylinders but reduce volume. If you increase the size of the wheel (slave) cylinder you increase pressure on the shoes/pads. Disk brake calipers require approx 1300 - 1500 psi to work correctly. Drum brakes require approx 400 - 600 psi to work correctly. The use of a proportioning valve assists in reducing pressure to the drum brakes if used on the rear. A Power booster is only another means of increasing pedal pressure to the master cylinder, if your pedal ratio is high enough you do not need a power booster, in most cars there is not enough room for the longer pedal, thus the power booster. I could be wrong, so if there is a brake expert out there please correct me.
Check your ratio prior to getting a master cylinder. Need to figure out the measurement from pivot point to rod attachment vs. pivot point to center of pedal. That will help determine if it will work well with or without a booster. Since the car was most likely manual brakes before, the ratio should be OK for a manual and a 1.125" bore. The Astro van master that your brakes came from used a 1.3" bore.
The original m/c was 1" bore, adding disc brakes will require a bit more pedal effort. I would not go bigger than 1" with manual brakes. Pedal effort gets pretty high.
Listen to the Squirrel!! Plus, you can try a 15/16" master, but you will have greater pedal travel owning to moving less fluid per stroke. The effect will be similar to power brakes, IF it will work with the increased travel. Normally the best plan starts with matching the front calipers to the master, but if you're going from power to manual (which I prefer), you need to step the master down in bore size. Oddly, it matters naught from single to dual reservoir master, bore size is bore size. Cosmo
The Jalopy Journal
